1. Field of the Invention
The present invention relates to a wide-angle zoom lens system suitable for a single lens reflex (SLR) camera, and relates to a wide-angle zoom lens system suitable for a digital SLR camera using a small imaging device (e.g., a CCD) which is smaller than a Leica-format size.
2. Description of the Prior Art
A CCD, having a Leica image-format size (36 mm×24 mm; hereinafter, the Leica-format size) which is the most widely-used format size in a SLR camera in which a silver halide film is used, is very expensive. Accordingly, a CCD having a format size which is about 0.7 times as large as the Leica-format size with respect to the image-height ratio is frequently used in a digital single reflex camera. Therefore if the format size becomes smaller, a lens system having a shorter focal length is required in order to achieve a wider angle-of-view.
A wide-angle zoom lens system which achieves an angle-of-view of 80 degrees or more at the short focal length extremity has already been available in the market; however, the zoom ratio is only about 2.0. The wide-angle zoom lens systems disclosed in Japanese Unexamined Patent Publications No. 2001-318314 and 2001-83421 are examples of such a zoom lens system. Furthermore, the zoom lens systems disclosed in Japanese Unexamined Patent Publications No.2000-338397 and Hei-11-174328 have a zoom ratio of about 3.0; however, the angle-of-view is not sufficiently secured.